Bag closure apparatus

ABSTRACT

Apparatus for automatically creasing and folding the open ends of filled &#39;&#39;&#39;&#39;tin-tie&#39;&#39;&#39;&#39; bags. The apparatus includes opposed gripping belts for moving the bags linearly and continuously through creasing and trimming stations at which rollers form two creases in and trim the sheet material of the end section of each bag and then through two folding stations each of which folds the end section upon itself about one of the creases.

United States Patent 1 1 Eburn, Jr. et a1.

1111 3,861,123 [451 Jan. 21, 1975 1 BAG CLOSURE APPARATUS [76] Inventors: William H. Eburn, Jr., 107 Hills Point Rd.; Charles T. Raymond, 15 Covelee Dr., both of Westport,

Conn. 06880 [22] Filed: July 24, 1972 [21] Appl. N0.: 274,471

[52] US. Cl 53/372, 53/378, 83/501 [51] Int. Cl B651) 7/08 [58] Field of Search 53/372, 378, 14, 46, 139,

[56] References Cited UNITED STATES PATENTS 1,911,136 5/1933 A11ison..... 53/371 X 2,700,260 1/1955 Paulsen 53/372 3,054,242 9/1962 Harrison et a1. 53/378 3,381,448 5/1968 Ayres et a1 53/46 X 3,417,543 12/1968 Jones, Jr. 53/372 X 3,621,746 11/1971 Womack 83/501 X Primary Examiner-Travis S. McGehee Assistant ExaminerH0race M. Culver Attorney, Agent, or Firm-St. Onge, Mayers, Steward & Reens [57] ABSTRACT Apparatus for automatically creasing and folding the open ends of filled tin-tie bags. The apparatus includes opposed gripping belts for moving the bags linearly and continuously through creasing and trimming stations at which rollers form two creases in and trim the sheet material of the end section of each bag and then through two folding stations each of which folds the end section upon'itself about one of the creases.

7 Claims, 16 Drawing Figures PATENTED JAN21 I975 SHEET 2 BF 6 PATENTED JANZI I975 SHEET 5 OF 6 FIG.6A

' FIG 6B PATENTED W21 3, 86 1 ,123

All/IE BAG CLOSURE APPARATUS BACKGROUND OF THE INVENTION 1. Field of Invention The present invention relates to closing bags and forming a so-called tin-tie" seal and particularly with a novel apparatus for and method of folding the open end section of the formed and filled bag twice upon itself to seal the bag.

2. Prior Art Bags and tin-tie closures of the type with which the present invention is concerned have been well known and widely used for many years. Essentially, the bag is of conventional shape having an open end with a rectangular cross section and preferably formed of a flexible sheet material which is substantially airand/or moisture-impermeable, examples of which include waxed paper, metallic foils, plastic films and multi-ply materials including paper, metallic foils and/or polymeric films. The bags are filled and the sides, at the open end, are tucked inwardly and compressed to form a multiple layer end section which is essentially planar in form and appearance. It is in this form that the bag is delivered to the apparatus for forming the tin-tie seal at the open end section. Tin-tie seals take their name from the use, in the past, of-a strip of sheet material, particularly a metal such as tin or tin-plated steel which can. be bent and retains its shape, attached to the bag end section for retaining it in a closed and sealed condition. The tin-tie strip shown comprises a flexible but non-resilient strip of an artificial plastic in which are embedded two wires for added strength and stiffness. The tin-tie closure is formed by adhering an elongated tin-tie strip to one face of the bag end section intermediate the end edge of the bag and the enlarged and filled portion thereof. The tin-tie strip is longer than the width of the bag end section so that the ends of the tintie strip extend therebeyond. The end portion of the bag is then folded a first time upon itself and the tin-tie strip so that the latter is sandwiched between portions of the end section which is folded a second time upon itself to form a reliable and substantially airand moisture-impermeable seal. The ends of the tin-tie strip are then folded back upon themselves and the bag end section to retain the latter in the folded, sealed condition.

Although automatic machinery has been developed and employed to form tin-tie bag closures, their operation has been slow and/or intermittent while the closures formed thereby are often irregular and/or fail in their function to seal the bag as well as to remain secure. Included among the most important operations involved in forming the bag closure are trimming the end section to proper length and then folding the end section upon itself twice to form a secure seal. Both operations must be performed accurately to produce the required seal and rapidly in order to achieve economical production rates. Combining speed with accuracy has heretofore proven difficult if not impossible to achieve, particularly with structures that are relatively simple and hence inexpensive, easy to fabricate and assemble, reliable in operation and simple to maintain.

BRIEF DESCRIPTION OF THE INVENTION Objects of the invention are: to provide novel and improved methods and apparatus for trimming and twice folding a bag end section upon itself as part of a tin-tie bag closure process; and to provide methods and apparatus of the type described characterized by their adaptability to continuous, rapid, accurate and reliable operation resulting in secure closures as well as a minimum of spoilage.

These and other objects of the invention are realized in a system in which the end sections of filled bags are moved continuously, rapidly and in close sequence through three machine stations which simultaneously trim and crease the end sections along two parallel spaced lines, and then bend each bag end section along one crease and then the other. Trimming and creasing in a single continuous operation insures both accurately located folds as well as sharp folds which contribute to a more secure seal. Novel and improved means are provided for creasing, trimming and folding the bag end sections as they are moved continuously and rapidly through the three stations whichperform these operations. The structures involved are relatively simple and easy to fabricate, assemble, and maintain in adjustment and repair. They are designed to require very little maintenance and make part replacement, when required, simple and rapid thereby minimizing machine down time and lost production.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the method involving the several steps and the relation and order ofone or more of such steps with respect to each of the others and the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclo sure, and the scope of the application of which will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is an elevational view looking in the direction of bag movement, of apparatus constructed in accor dance with the invention for moving, creasing and trimming bag end sections, and illustrating the method of the invention;

FIG. 2 is an enlarged view of the creasing and trimming means of FIG. 1;

FIG. 3 is an elevational view similar to FIG. 1, illustrating a bag end section folding station;

FIG. 4 is an exploded, elevational view, partially in section, of the components of a folding station;

FIGS. 5A through 5F are sections taken substantially along the lines 5A5A through 5F5F of FIG. 4;

FIGS. 6A through 6E are sectional views, similar to 5A through SE, of the other folding station; and

FIG. 7 is a perspective view of a folding station.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The present invention is incorporated in three stations of a bag closing machine and means for gripping the bags to hold them closed while moving the bag end sections through the three stations. The bags arrive at the first of these stations with tin-tie strips already attached to the end sections of the bags. At the first station, each bag end section is trimmed along a line and is simultaneously creased along two parallel lines substantially equally spaced from one another and the trimmed edge and parallel therewith. At the next station, the end section is folded upon itself about the crease closest the end edge so that the tin-tie strip is sandwiched between two portions of the end section. At the next station, the bag end section is again folded upon itself, this time along the other crease so that the end portion of the end section between the edge and first'crease is sandwiched between another portion of the end section and the tin-tie strip. From the second folding station, the bag is moved by the same gripping means through another station (not shown) for bending the projecting ends of the tin-tie strip to retain the bag end section in its folded and sealed condition. Throughout all of these operations, the bag end sections are moved continuously, linearly and at relatively high speed to achieve maximum production rates.

Reference is now made to FIGS. 1 and 2 of the drawings wherein there is illustrated means constructed in accordance with the invention forcreasing and trimming the end section, generally designated 10, of a bag and means for gripping and continuously advancing the bag during creasing and trimming operations. The

means for gripping the bag to hold it closed and ad-.

vancing the bag continuously and at relatively high speed during at least the creasing and folding operations comprise a pair of endless belts designated 12 and 14. Belts l2 and 14 are driven by conventional V-drive pulleys (not shown) and are supported in compressive engagement with the end section of a bag and guided along linear paths by a multiplicity of adjacent backing wheels 16 and 18. Wheels 16 (only one is shown) are mounted in a row in fixed position while wheels 18 are mounted in another parallel row, each on a shaft 20 supported on a spring-loaded crank arm 22 for biasing belt 14 (upwardly viewing FIG. 1) toward belt 12. Belts l2 and 14 are preferably of a conventional fiber-reinforced, rubber construction characterized by a high'friction coefficient.

For the sake of convenience of illustration, the main portion, designated 24, of a bag and end section 10 thereof are shown as being located horizontally whereas, in actual practice, the bag will be inclined at an angle of about 60 from the vertical or 30 from the horizontal so that the main portion is lower than the end section to be closed. An inclined support plate 26 is provided for supporting the bag on its lower side (not bottom) so that the bag is, in effect, suspended by belts l6 and 1 8 ,which prevent it from sliding down the surface of inclined support plate 26. Similarly, many of the other components of the apparatus, including those yet to be described, are also inclined with respect to horizontal, but are shown in the drawings as being horizontal.

To further facilitate illustration, as well as ease of understanding of the invention, those components embodying the invention are shown in detail while many other mechanical components such as gears, chain drives, sprockets, links, cams, bearings and the like, having known, conventional constructions and being frequently available as standard components or assemblies, have been omitted from the drawings and/or the accompanying description.

Belts l2 and 14 not only hold the bag closed, but also function to support the end sections of the layers of sheet material of the bag substantially in a plane while moving the sheet material layers of the bag end section 4 linearly substantially in the plane thereof through subsequent machine stations wherein closure operations are performed on the end section of the bag. As previously noted, those operations with which the present invention is concerned include trimming the end edge of the bag so that it is parallel with the direction of movement; creasing the bag along two parallel lines substantially equally spaced from one another and the end edge of the bag; and then folding the end section upon itself twice in the samedirection, first about the crease closest the edge and then about the other crease.

As shown in FIGS. 1 and 2, the invention includes a novel and improved system for simultaneously shearing the end of the bag and forming two, parallel, V-shaped (in cross-section) creases in the layers of sheet material comprising the end section of the bag. The creasing means, viewed in the direction of bag motion, comprise a pair of creasing rollers designated 30 and 40. Rollers 30 and 40 have substantially cylindrical peripheral surfaces designated, respectively, 32 and 42, and' are mounted for rotation about parallel axes on shafts 3 4 and '44, respectively. Roll 30 is substantially fixed against axial motion in one direction-(toward the left, viewing FIG. 1) while roll 40 and its mounting shaft 44 are free to move axially.

Conventional drive means including gears 36 and 46 keyedto shafts 34 and 44, respectively, are provided for rotating the rolls at a speed such that the linear velocity of peripheral surfaces 32 and 42'substantially matches the speed of motion of bags gripped between belts l2 and 14. Rolls '30 and 40 are positioned such is formed withmatching, aligned peripheral grooves 38. Rolls 30 and 40 are mounted with respect to one another so as to cooperate to form a convergent passage having a fixed depth at least equal to and preferably slightly greater than the combined thicknesses of the layers of sheet material of the end section of the bag. The ribs (and grooves) are parallel and lie in a plane perpendicular to the rotational axes of the rolls so that as the layers of sheet material comprising the end section of a bag are moved therebetween, the rib force the sheet material into the grooves (as shown in detail in'FIG. 2) forming V-shaped creases in the bag.

At the same time the bag end section is being creased, it is also being cut to proper length along a line parallel with the creases and spaced from the nearest crease about the same distance as the spacing between creases. For this purpose, roll 30 is provided with a shearing disc 50 formed of a hardened material, (steel) and having a peripheral surface 52 forming an extension of surface 32, a sharpened edge 54 and an end surface 56 lying in a plane perpendicular to the rotational axis of roll 30. Roll 40 is provided with a similar shearing disc'58 having a diameter greater than roll 40 so that it overlaps disc 50, and is formed with a planar surface 60 lying in the same plane as surface 56 and a I sharpened cutting edge 62 adapted to cooperate with edge 54 to function as a rotary shear. A spring 63 is. provided coiled around shaft 44 for biasing shearing disc 58 axially against the end face 56 of disc 50 to insure close contact and shearing action. Both discs 50 and 58 are attached to the ends of rolls 30 and 40 by suitable means such as machine screws 64 so that they may be readily detached from the rolls for the purpose of sharpening or replacement as required.

A major problem with attempting to crease and shear the end portions of moving bags by employing creasing rollers is mistracking as the end portion is advanced between the rolls. It is essential that the bag be trimmed and creased along lines extending at least approximately perpendicular to the parallel leading and trailing edges of end portion 10, otherwise there may be insufficient material available to make the bends required to seal the bag. As previously noted, in the past those skilled in the art have either avoided creasing the bag prior to folding or have experienced severe mistracking difficulties due to the fact that once the bag enters the bite of a pair of pressure-applying rollers, it will continue to advance perpendicular to the axis of the rollers. Thus, if the bag enters at a slight angle, it will continue to be advanced at that angle resulting in axial movement of the bag relative to the rollers and formation of creases extending transverse the bag at the same'angle. If axial motion is away from the belts, then the result may well be tearing of the bag where it is gripped between belts 12 and 14, while movement toward the belt may be such that the untrimmed edge is withdrawn beyond the shears and remains untrimmed and/or there is insufficient material available for forming a properly folded seal.

In accordance with the invention, the answer to this problem has been found to lie in spacing the rollers by a minimum distance at least equal to and preferably greater than the aggregate thicknesses of the layers of bag material comprising end section so that the bag is not under compression by the rollers. By virtue of this construction, the direction of bag movement between the creasing rollers, as well as the position of the creases and the trimmed edge, is controlled by belts 12 and 14 which, in turn, are carefully guided by rollers 16 and 18. Thus, any misalignment of the end section 10 as it enters the bite of the creasing rolls may be corrected during passage therebetween and is not compounded or made worse by subsequent mistracking. In an alternative embodiment, an annular portion of the periphery 46 of roll 40 intermediate ribs 48 may be recessed slightly to provide additional clearance for a conventional tin-tie strip designated 66. The creasing rollers are rotated to facilitate movement of the bags by belts 12 and 14 eliminating relative motion and reducing friction rather than for the purpose of advancing the bags.

The apparatus includes novel and improved means immediately downstream from the creasing rolls for accurately folding the bag twice upon itself at the creases to form a substantially airtight seal. The folding means include two folding stations or sets of folding members each similar to the other and each designed to impart a 180 fold to the bag end section 10 as the bag is moved continuously. FIGS. 3 and 4 show the construction of the second folding station which is essentially the same as the first folding station located upstream thereof. As shown in FIG. 3, the second folding station basically comprises two elongated folding members designated 80 and 90 mounted in juxtaposed relation. Members 80 and 90 are each formed with a helical folding surface designated, respectively, 82 and 92 located in spaced relation and cooperating to form a helical slot for engaging the sides of the portion of section 10 adapted to be folded about a crease. Folding member is mounted in fixed position and includes a planar guide surface 84 located in a plane substantially coincident with the one surface (lower in FIG. 3) of section 10 for supporting and guiding the portion of section 10 intermediate belts l2 and 14 and the crease about which the end section is being folded. Surface 84 intersects folding surface 82 at a line or intersection designated 86 extending parallel with the direction of bag motion and coinciding with the innermost crease in the end section 10 of the bag. Surface 82 is substantially helical in form rotating through 180 from its upstream end to its downstream end so that it faces in opposite directions at opposite ends and the bag is folded about the edge or line of intersection 86 of helical surface 82 and guide surface 84.

Folding member 90 is formed with a helical surface 92 similar to surface 82 and, in the operative or closed position of the folding members, disposed in face-toface spaced relation with surface 82 to form a guide or helical folding slot designated 100. Folding member 90 also includes a guide surface 94 similar to guide surface 84 and located in spaced, parallel relation for engaging the other (upper) surface of end section 10 and cooperating with surface 84 to form a guide slot generally designated 102. FIGS. 5A through 5F are sections taken through the folding members viewed in a direction opposite to the direction of bag motion showing the cross-sectional configuration of the members as well as the orientation of helical slot and guide slot 102. FIG. 5A is a section taken near the upstream end of the members, and FIGS. 53, 5C, 5D and 5E are taken at 45 intervals along the helical folding slot to illustrate the 180 bending of the bag end section. The first or upstream pair of bag folding members designated and are similar in construction and function to members 80 and 90 and are shown in section in FIGS. 6A through 6E (similar to FIGS. 5A through 5E). Member 1 10 includes a helical folding surface 1 12 intersecting a guide surface 114 at a line or edge 116 located at the end crease, surface 114 being formed with a channel 118 for accommodating the added thickness of tin-tie strip 60. Folding member 120 includes a helical folding surface 122 and a planar guide surface 124 cooperating with surfaces 112 and 114, respectively, to form a helical folding slot 104 and a planar guide slot 106.

Folding members 80 and 110 are mounted in substantially fixed positions relative to the path of movement of the bag end sections 10. Members 90 and 120 are mounted for movement relative to members 80 and 110 between the operative or closed positions shown, and inoperative or open positions in which the members of each pair are spaced apart to permit replacement, cleaning, freeing of jams, and the like. In order to accomplish this relative motion, the movable members are mounted for both rotary and linear motion since portions of the movable members, in the operative position, are located on opposite sides of the fixed members.

The mounting means for movable folding members 90 and 120 are substantially identical and are shown by way of example in FIGS. 3 and 7 in which one such structure is illustrated. The mounting means comprises a shaft 130 mounted for rotary and axial motion in a fixed support 132 with the axis of the shaft located substantially in a plane (shown as horizontal) parallel with the plane of movement of end section 10. Each of the movable guide members 90 and 120 is mounted on a shaft 130 approximately at its mid-point. Extending from the upstream end of each of movable members 90 and 120 is a cam slot plate 136 extending parallel with shaft 130 away from the movable guide member and formed with a generally U-shaped cam slot 138 having a medial section 140 substantially parallel with shaft 130, and end section 142 inclined at approximately a 45 angle and another end section 144 extending from the medial section at a 90 angle. A fixed pin or cam 146 is mounted on support 132 so as to extend into cam slot 138 where it is engaged for sliding motion.

Thus, during initial opening or withdrawal motion of the movable folding member, it is rotated by virtue of engagement of pin 146 in section 142 of slot 138 such that the upstream end of the movable member is moved away from the fixed member so that the portion of the movable member located on the bag side of the fixed member will clear the latter when retracted. This motion is such that the helical surfaces tend to remain in facing or parallel relation as they are moved apart. The intermediate section 140 of slot 138 provides for linear and slight rotary motion, while end section 144 of the slot enables the shaft and folding member mounted thereon to be pivoted in the opposite direction into a position at which the movable member is retained or locked against motion toward the fixed member. A knob 152 is mounted on the cam slot plate 136 to facilitate manual movement of it, the shaft and the folding member mounted thereon. An enlarged knob 134 is provided on the end of shaft 130 to facilitate manual rotation thereof.

Of course, as the upstream end of the movable member is pivoted away from the fixed member, the other or downstream end moves in the opposite direction. In order to permit this to occur while providing a fulllength guide surface (94 or 124), i.e., equal in length to the fixed member, on the movable member, the latter is provided with a guide plate designated 98 or 128. In the form shown in FIGS. 3 through 5, guide plate 98 is approximately half the length of folding member 90 and, in its operative position, forms an extension of the portion of the folding member providing guide surface 94. Guide plate 98 (or 128 as the case may be) is mounted for pivotal movement on bag folding member 90 (or 120) between the operative or closed position (shown in FIGS. 3 and to an open position (shown in broken lines in FIG. 3) to provide sufficient clearance to permit the movable folding member to be pivoted as described. A cam lever 160 is coupled to guide plate 98 and engaged with a curved retaining spring 162 for retaining the guide plate in both its open position and its closed or operative position. An elongated handle 164 is also attached to the guide plate to facilitate pivotal movement thereof manually.

The structure described accomplishes the objects of the invention in that it provides reliable means for rapidly and accurately trimming and folding the end sections of a succession of continuously moving bags. The individual components which contact and manipulate the bags are easy to fabricate and assemble, as well as to service and replace as required. Accurate and sharp folding and resultant improved sealing are assured by creasing the bag end sections. This, in turn, is achieved by a novel roller structure and method which eliminate mistracking that would otherwise result in damaged bags or improper folds and seals. The apparatus is designed to be operated continuously at high linear bag transport speeds with an accordingly high production rate.

Since certain changes may be made in the above method and apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In apparatus for closing the open end ofa filled bag including opposed gripping means for engaging the sheet material comprising the end sectionof a bag at a location inwardly from the end edge thereof to hold the layers of sheet material comprising the end section of the bag in closed, face-to-face relation substantially in a plane, the improvement comprising, in combination: A. a pair ofjuxtaposed creasing means positioned to engage between them the end section of a bag held by said gripping means;

B. means for moving said gripping means linearly and continuously to move the end section of a bag, substantially in the plane of the end section and sub-' stantially parallel with the edge thereof, between said creasing means;

C. one of said creasing means providing a pair of spaced, parallel grooves extending in the direction of linear movement of the end section of a bag held and advanced by said gripping means;

D. the other of said creasing means providing ribs aligned with and projecting into said grooves for engaging and creasing the end section of a bag along spaced, parallel lines during movement thereof between said creasing means;

E. first folding means positioned in the path of movement of the creased end section of a bag for folding the end section upon itself about the crease closest the end edge thereof; and

F. second folding means positioned downstream from said first folding means for folding the folded end section in the same direction upon itself about the other crease; each of said folding means comprismg:

i. first and second folding members having adjacent, spaced surfaces defining therebetween a slot having an upstream end section located in the path of movement of the end section ofa bag held and advanced by said gripping means, said members having generally planar guide surfaces for engaging a portion of the end section adjacent the portion to be folded;

a. said planar surface of said first member terminating in a linear edge located in alignment with one of said ribs and grooves and the direction of movement of a bag end section, and defining the edge of a first helical folding surface, the latter facing in the same direction as said guide surface at the upstream end of said first member and gradually rotating through l about said edge to face in the opposite direction at the downstream end of said first member;

b. said second member including a second helical surface located in spaced, face-to-face relation with said first helical surface to form a helical slot for engaging the end portion of the end section of a bag to fold the end section upon itself at a crease therein; and

c. one of each pair of folding members being mounted in substantially fixed position, and the other member of the pair being mounted for simultaneous rotary and linear movement relative to and apart from the member with which it is associated.

2. Bag closing apparatus according to claim 1 wherein the mounting means for each movable member includes a shaft mounted for rotary and axial motion and the movable member is mounted on said shaft substantially midway between the ends of said second helical folding surface.

3. Bag closing apparatus according to claim 2 wherein each of said shafts is mounted with its axis located in a plane at least parallel with the planes of said guide surfaces and normal to the direction of movement of said gripping means.

4. Bag closing apparatus according to claim 3 wherein each of said mounting means includes means for rotating said shaft during axial motion thereof such that said first and second helical surfaces remain in substantially parallel relation as they are moved relative to one another.

5. Bag closing apparatus according to claim 1 wherein the portion of each of said second members providing said guide surface terminates approximately midway along said second helical surface at a point where the latter is rotated approximately and each of said folding means includes a guide plate movably mounted on the downstream section of said each second folding member for providing a continuation of said guide surface thereof extending substantially to the downstream end of said helical surface of said second member.

6. Bag closing apparatus according to claim 5 wherein said each second member is mounted for rotary and axial movement approximately midway between its ends and said guide plate is mounted for pivotal movement away from said first member from an operative position in which it provides a continuation of said guide surface to a displaced position at which it cannot interfere with rotary and linear motion of said second member relative to said first member.

7. Bag closing apparatus according to claim 6 further including means mounted on each of said second members for releasably retaining said guide plate-mounted thereon in either the operative or displaced position 

1. In apparatus for closing the open end of a filled bag including opposed gripping means for engaging the sheet material comprising the end section of a bag at a location inwardly from the end edge thereof to hold the layers of sheet material comprising the end section of the bag in closed, face-to-face relation substantially in a plane, the improvement comprising, in combination: A. a pair of juxtaposed creasing means positioned to engage between them the end section of a bag held by said gripping means; B. means for moving said gripping means linearly and continuously to move the end section of a bag, substantially in the plane of the end section and substantially parallel with the edge thereof, between said creasing means; C. one of said creasing means providing a pair of spaced, parallel grooves extending in the direction of linear movement of the end section of a bag held and advanced by said gripping means; D. the other of said creasing means providing ribs aligned with and projecting into said grooves for engaging and creasing the end section of a bag along spaced, parallel lines during movement thereof between said creasing means; E. first folding means positioned in the path of movement of the creased end section of a bag for folding the end section upon itself about the crease closest the end edge thereof; and F. second folding means positioned downstream from said first folding means for folding the folded end section in the same direction upon itself about the other crease; each of said folding means comprising: i. first and second folding members having adjacent, spaced surfaces defining therebetween a slot having an upstream end section located in the path of movement of the end section of a bag held and advanced by said gripping means, said members haviNg generally planar guide surfaces for engaging a portion of the end section adjacent the portion to be folded; a. said planar surface of said first member terminating in a linear edge located in alignment with one of said ribs and grooves and the direction of movement of a bag end section, and defining the edge of a first helical folding surface, the latter facing in the same direction as said guide surface at the upstream end of said first member and gradually rotating through 180* about said edge to face in the opposite direction at the downstream end of said first member; b. said second member including a second helical surface located in spaced, face-to-face relation with said first helical surface to form a helical slot for engaging the end portion of the end section of a bag to fold the end section upon itself at a crease therein; and c. one of each pair of folding members being mounted in substantially fixed position, and the other member of the pair being mounted for simultaneous rotary and linear movement relative to and apart from the member with which it is associated.
 2. Bag closing apparatus according to claim 1 wherein the mounting means for each movable member includes a shaft mounted for rotary and axial motion and the movable member is mounted on said shaft substantially midway between the ends of said second helical folding surface.
 3. Bag closing apparatus according to claim 2 wherein each of said shafts is mounted with its axis located in a plane at least parallel with the planes of said guide surfaces and normal to the direction of movement of said gripping means.
 4. Bag closing apparatus according to claim 3 wherein each of said mounting means includes means for rotating said shaft during axial motion thereof such that said first and second helical surfaces remain in substantially parallel relation as they are moved relative to one another.
 5. Bag closing apparatus according to claim 1 wherein the portion of each of said second members providing said guide surface terminates approximately midway along said second helical surface at a point where the latter is rotated approximately 90*, and each of said folding means includes a guide plate movably mounted on the downstream section of said each second folding member for providing a continuation of said guide surface thereof extending substantially to the downstream end of said helical surface of said second member.
 6. Bag closing apparatus according to claim 5 wherein said each second member is mounted for rotary and axial movement approximately midway between its ends and said guide plate is mounted for pivotal movement away from said first member from an operative position in which it provides a continuation of said guide surface to a displaced position at which it cannot interfere with rotary and linear motion of said second member relative to said first member.
 7. Bag closing apparatus according to claim 6 further including means mounted on each of said second members for releasably retaining said guide plate mounted thereon in either the operative or displaced position thereof. 